Predicting subject body poses and subject movement intent using probabilistic generative models

ABSTRACT

Certain aspects of the present disclosure are directed to methods and apparatus for predicting subject motion using probabilistic models. One example method generally includes receiving training data comprising a set of subject pose trees. The set of subject pose trees comprises a plurality of subsets of subject pose trees associated with an image in a sequence of images, and each subject pose tree in the subset indicates a location along an axis of the image at which each of a plurality of joints of a subject is located. The received training data may be processed in a convolutional neural network to generate a trained probabilistic model for predicting joint distribution and subject motion based on density estimation. The trained probabilistic model may be deployed to a computer vision system and configured to generate a probability distribution for the location of each joint along the axis.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to artificial neural networksand, more particularly, to using probabilistic generative models in anartificial neural network to predict subject body poses and subjectmovement intent.

DESCRIPTION OF RELATED ART

An artificial neural network, which may be composed of an interconnectedgroup of artificial neurons (e.g., neuron models), is a computationaldevice or represents a method performed by a computational device. Theseneural networks may be used for various applications and/or devices,such as Internet Protocol (IP) cameras, Internet of Things (IoT)devices, autonomous vehicles, and/or service robots.

Convolutional neural networks are a type of feed-forward artificialneural network. Convolutional neural networks may include collections ofartificial neurons that each have a receptive field and thatcollectively tile an input space. Convolutional neural networks (CNNs)have numerous applications. In particular, CNNs have broadly been usedin the area of pattern recognition and classification.

In layered neural network architectures, the output of a first layer ofartificial neurons becomes an input to a second layer of artificialneurons, the output of a second layer of artificial neurons becomes aninput to a third layer of artificial neurons, and so on. Convolutionalneural networks may be trained to recognize a hierarchy of features.Computation in convolutional neural network architectures may bedistributed over a population of processing nodes, which may beconfigured in one or more computational chains. These multi-layeredarchitectures may be trained one layer at a time and may be fine-tunedusing back propagation. Advances in technology have resulted in smallerand more powerful computing devices. The prevalence of these computingdevices is driven in part by the many functions that are now enabled onsuch devices. Demand for such functions increases processing capabilityrequirements and, in some cases, generates a need for more powerfulbatteries. Within the limited space of the housing of these computingdevices, batteries compete with the processing circuitry. These andother factors contribute to a continued miniaturization of componentswithin the circuitry.

BRIEF SUMMARY

Certain aspects of the present disclosure are directed to a method forpredicting subject motion. The method generally includes receivingtraining data comprising a set of subject pose trees, wherein the set ofsubject pose trees comprises a plurality of subsets of subject posetrees, wherein each subset of subject pose trees is associated with animage in a sequence of images, and wherein each subject pose tree in thesubset is associated with an axis of the image and indicates a locationalong the axis of the image at which each of a plurality of joints of asubject is located; processing the received training data in aconvolutional neural network to generate a trained probabilistic modelfor predicting joint distribution and subject motion based on densityestimation; and deploying the trained probabilistic model to a computervision system, wherein the trained probabilistic model is configured togenerate a probability distribution for each joint, the probabilitydistribution indicating a likelihood that the joint will be located ateach location along the axis.

Certain aspects of the present disclosure are directed to an apparatusfor predicting subject motion. The apparatus generally includes at leastone processor configured to receive training data comprising a set ofsubject pose trees, wherein the set of subject pose trees comprises aplurality of subsets of subject pose trees, wherein each subset ofsubject pose trees is associated with an image in a sequence of images,and wherein each subject pose tree in the subset is associated with anaxis of the image and indicates a location along the axis of the imageat which each of a plurality of joints of a subject is located. The atleast one processor is further configured to process the receivedtraining data in a convolutional neural network to generate a trainedprobabilistic model for predicting joint distribution and subject motionbased on density estimation and to deploy the trained probabilisticmodel to a computer vision system, wherein the trained probabilisticmodel is configured to generate a probability distribution for eachjoint, the probability distribution indicating a likelihood that thejoint will be located at each location along the axis. The apparatus mayfurther include a memory coupled to the at least one processor. Thememory may be configured to store at least one of the training data orthe probability distribution for each joint.

Certain aspects of the present disclosure are directed to an apparatusfor predicting subject motion. The apparatus generally includes meansfor receiving training data comprising a set of subject pose trees,wherein the set of subject pose trees comprises a plurality of subsetsof subject pose trees, wherein each subset of subject pose trees isassociated with an image in a sequence of images, and wherein eachsubject pose tree in the subset is associated with an axis of the imageand indicates a location along the axis of the image at which each of aplurality of joints of a subject is located; means for processing thereceived training data in a convolutional neural network to generate atrained probabilistic model for predicting joint distribution andsubject motion based on density estimation; and means for deploying thetrained probabilistic model to a computer vision system, wherein thetrained probabilistic model is configured to generate a probabilitydistribution for each joint, the probability distribution indicating alikelihood that the joint will be located at each location along theaxis.

Certain aspects of the present disclosure are directed to anon-transitory computer-readable medium. The non-transitorycomputer-readable medium generally includes instructions that, whenexecuted by at least one processor, configure the at least one processorto perform an operation for predicting subject motion. The operationgenerally includes receiving training data comprising a set of subjectpose trees, wherein the set of subject pose trees comprises a pluralityof subsets of subject pose trees, wherein each subset of subject posetrees is associated with an image in a sequence of images, and whereineach subject pose tree in the subset is associated with an axis of theimage and indicates a location along the axis of the image at which eachof a plurality of joints of a subject is located; processing thereceived training data in a convolutional neural network to generate atrained probabilistic model for predicting joint distribution andsubject motion based on density estimation; and deploying the trainedprobabilistic model to a computer vision system, wherein the trainedprobabilistic model is configured to generate a probability distributionfor each joint, the probability distribution indicating a likelihoodthat the joint will be located at each location along the axis.

Other aspects, advantages, and features of the present disclosure willbecome apparent after review of the entire application, including thefollowing sections: Brief Description of the Drawings, DetailedDescription, and the Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example implementation of a system-on-a-chip(SOC).

FIG. 2A illustrates an example of a fully connected neural network.

FIG. 2B illustrates an example of a locally connected neural network.

FIG. 2C illustrates an example of a convolutional neural network.

FIG. 2D illustrates a detailed example of a deep convolutional network(DCN) designed to recognize visual features from an image.

FIG. 3 is a block diagram illustrating a deep convolutional network(DCN).

FIG. 4 illustrates an example subject pose, a subject pose treegenerated from the subject pose, and a two-dimensional tensorrepresenting the subject pose tree, according to aspects presentedherein.

FIG. 5 illustrates an example stack of convolutional layers that may beused to generate an auto-regressive probabilistic model for predictingjoint distribution and subject motion, according to aspects presentedherein.

FIG. 6 illustrates example masks of data associated with joint motionused to train a probabilistic model for predicting joint distributionand subject motion, according to aspects presented herein.

FIG. 7 illustrates example operations for generating a probabilisticmodel for predicting joint distribution and subject motion based onsubject pose trees, according to aspects presented herein.

FIG. 8 illustrates example probability distributions and a heatmaprepresenting a predicted location of a joint, according to aspectspresented herein.

FIG. 9 illustrates an example stack of colorized joint motions that maybe used in determining a motion intent from a predicted subject motion,according to aspects presented herein.

FIG. 10 illustrates example operations for predicting future subjectmotion using an auto-regressive probabilistic model, according toaspects presented herein.

FIG. 11 shows a block diagram illustrating an exemplary softwarearchitecture for modularizing artificial intelligence (AI) functions,according to aspects presented herein.

DETAILED DESCRIPTION

With reference now to the Figures, several exemplary aspects of thepresent disclosure are described. The word “exemplary” is used herein tomean “serving as an example, instance, or illustration.” Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects.

Example Artificial Neural Networks

FIG. 1 illustrates an example implementation of a system-on-a-chip (SOC)100, which may include a central processing unit (CPU) 102 or amulti-core CPU configured to perform a parallel Monte Carlo dropoutfunction, in accordance with certain aspects of the present disclosure.Variables (e.g., neural signals and synaptic weights), system parametersassociated with a computational device (e.g., neural network withweights), delays, frequency bin information, and task information may bestored in a memory block associated with a neural processing unit (NPU)108, in a memory block associated with a CPU 102, in a memory blockassociated with a graphics processing unit (GPU) 104, in a memory blockassociated with a digital signal processor (DSP) 106, in a memory block118, or may be distributed across multiple blocks. Instructions executedat the CPU 102 may be loaded from a program memory associated with theCPU 102 or may be loaded from a memory block 118.

The SOC 100 may also include additional processing blocks tailored tospecific functions, such as a GPU 104, a DSP 106, a connectivity block110, which may include fifth generation (5G) connectivity, fourthgeneration long term evolution (4G LTE) connectivity, Wi-Ficonnectivity, USB connectivity, Bluetooth connectivity, and the like,and a multimedia processor 112 that may, for example, detect andrecognize gestures. In one implementation, the NPU is implemented in theCPU, DSP, and/or GPU. The SOC 100 may also include a sensor processor114, image signal processors (ISPs) 116, and/or navigation module 120,which may include a global positioning system.

The SOC 100 may be based on an ARM instruction set. In an aspect of thepresent disclosure, the instructions loaded into the CPU 102 maycomprise code to search for a stored multiplication result in a lookuptable (LUT) corresponding to a multiplication product of an inputfeature value and a filter weight. The instructions loaded into the CPU102 may also comprise code to disable a multiplier during amultiplication operation of the multiplication product when a lookuptable hit of the multiplication product is detected. In addition, theinstructions loaded into the CPU 102 may comprise code to store acomputed multiplication product of the input feature and the filterweight when a lookup table miss of the multiplication product isdetected.

Deep learning architectures may perform an object recognition task bylearning to represent inputs at successively higher levels ofabstraction in each layer, thereby building up a useful featurerepresentation of the input data. In this way, deep learning addresses amajor bottleneck of traditional machine learning. Prior to the advent ofdeep learning, a machine learning approach to an object recognitionproblem may have relied heavily on human engineered features, perhaps incombination with a shallow classifier. A shallow classifier may be atwo-class linear classifier, for example, in which a weighted sum of thefeature vector components may be compared with a threshold to predict towhich class the input belongs. Human engineered features may betemplates or kernels tailored to a specific problem domain by engineerswith domain expertise. Deep learning architectures, in contrast, maylearn to represent features that are similar to what a human engineermight design, but through training. Furthermore, a deep network maylearn to represent and recognize new types of features that a humanmight not have considered.

A deep learning architecture may learn a hierarchy of features. Ifpresented with visual data, for example, the first layer may learn torecognize relatively simple features, such as edges, in the inputstream. In another example, if presented with auditory data, the firstlayer may learn to recognize spectral power in specific frequencies. Thesecond layer, taking the output of the first layer as input, may learnto recognize combinations of features, such as simple shapes for visualdata or combinations of sounds for auditory data. For instance, higherlayers may learn to represent complex shapes in visual data or words inauditory data. Still higher layers may learn to recognize common visualobjects or spoken phrases.

Deep learning architectures may perform especially well when applied toproblems that have a natural hierarchical structure. For example, theclassification of motorized vehicles may benefit from first learning torecognize wheels, windshields, and other features. These features may becombined at higher layers in different ways to recognize cars, trucks,and airplanes.

Neural networks may be designed with a variety of connectivity patterns.In feed-forward networks, information is passed from lower to higherlayers, with each neuron in a given layer communicating to neurons inhigher layers. A hierarchical representation may be built up insuccessive layers of a feed-forward network, as described above. Neuralnetworks may also have recurrent or feedback (also called top-down)connections. In a recurrent connection, the output from a neuron in agiven layer may be communicated to another neuron in the same layer. Arecurrent architecture may be helpful in recognizing patterns that spanmore than one of the input data chunks that are delivered to the neuralnetwork in a sequence. A connection from a neuron in a given layer to aneuron in a lower layer is called a feedback (or top-down) connection. Anetwork with many feedback connections may be helpful when therecognition of a high-level concept may aid in discriminating theparticular low-level features of an input.

The connections between layers of a neural network may be fullyconnected or locally connected. FIG. 2A illustrates an example of afully connected neural network 202. In a fully connected neural network202, a neuron in a first layer may communicate its output to everyneuron in a second layer, so that each neuron in the second layer willreceive input from every neuron in the first layer. FIG. 2B illustratesan example of a locally connected neural network 204. In a locallyconnected neural network 204, a neuron in a first layer may be connectedto a limited number of neurons in the second layer. More generally, alocally connected layer of the locally connected neural network 204 maybe configured so that each neuron in a layer will have the same or asimilar connectivity pattern, but with connections strengths that mayhave different values (e.g., 210, 212, 214, and 216). The locallyconnected connectivity pattern may give rise to spatially distinctreceptive fields in a higher layer, because the higher layer neurons ina given region may receive inputs that are tuned through training to theproperties of a restricted portion of the total input to the network.

One example of a locally connected neural network is a convolutionalneural network. FIG. 2C illustrates an example of a convolutional neuralnetwork 206. The convolutional neural network 206 may be configured suchthat the connection strengths associated with the inputs for each neuronin the second layer are shared (e.g., 208). Convolutional neuralnetworks may be well suited to problems in which the spatial location ofinputs is meaningful.

One type of convolutional neural network is a deep convolutional network(DCN). FIG. 2D illustrates a detailed example of a DCN 200 designed torecognize visual features from an image 226 input from an imagecapturing device 230, such as a car-mounted camera. The DCN 200 of thecurrent example may be trained to identify traffic signs and a numberprovided on the traffic sign. Of course, the DCN 200 may be trained forother tasks, such as identifying lane markings or identifying trafficlights.

The DCN 200 may be trained with supervised learning. During training,the DCN 200 may be presented with an image, such as the image 226 of aspeed limit sign, and a forward pass may then be computed to produce anoutput 222. The DCN 200 may include a feature extraction section and aclassification section. Upon receiving the image 226, a convolutionallayer 232 may apply convolutional kernels (not shown) to the image 226to generate a first set of feature maps 218. As an example, theconvolutional kernel for the convolutional layer 232 may be a 5×5 kernelthat generates 28×28 feature maps. In the present example, because fourdifferent feature maps are generated in the first set of feature maps218, four different convolutional kernels were applied to the image 226at the convolutional layer 232. The convolutional kernels may also bereferred to as filters or convolutional filters.

The first set of feature maps 218 may be subsampled by a max poolinglayer (not shown) to generate a second set of feature maps 220. The maxpooling layer reduces the size of the first set of feature maps 218.That is, a size of the second set of feature maps 220, such as 14×14, isless than the size of the first set of feature maps 218, such as 28×28.The reduced size provides similar information to a subsequent layerwhile reducing memory consumption. The second set of feature maps 220may be further convolved via one or more subsequent convolutional layers(not shown) to generate one or more subsequent sets of feature maps (notshown).

In the example of FIG. 2D, the second set of feature maps 220 isconvolved to generate a first feature vector 224. Furthermore, the firstfeature vector 224 is further convolved to generate a second featurevector 228. Each feature of the second feature vector 228 may include anumber that corresponds to a possible feature of the image 226, such as“sign,” “60,” and “100.” A softmax function (not shown) may convert thenumbers in the second feature vector 228 to a probability. As such, anoutput 222 of the DCN 200 is a probability of the image 226 includingone or more features.

In the present example, the probabilities in the output 222 for “sign”and “60” are higher than the probabilities of the others of the output222, such as “30,” “40,” “50,” “70,” “80,” “90,” and “100”. Beforetraining, the output 222 produced by the DCN 200 is likely to beincorrect. Thus, an error may be calculated between the output 222 and atarget output. The target output is the ground truth of the image 226(e.g., “sign” and “60”). The weights of the DCN 200 may then be adjustedso the output 222 of the DCN 200 is more closely aligned with the targetoutput.

To adjust the weights, a learning algorithm may compute a gradientvector for the weights. The gradient may indicate an amount that anerror would increase or decrease if the weight were adjusted. At the toplayer, the gradient may correspond directly to the value of a weightconnecting an activated neuron in the penultimate layer and a neuron inthe output layer. In lower layers, the gradient may depend on the valueof the weights and on the computed error gradients of the higher layers.The weights may then be adjusted to reduce the error. This manner ofadjusting the weights may be referred to as “back propagation” as itinvolves a “backward pass” through the neural network.

In practice, the error gradient of weights may be calculated over asmall number of examples, so that the calculated gradient approximatesthe true error gradient. This approximation method may be referred to asstochastic gradient descent. Stochastic gradient descent may be repeateduntil the achievable error rate of the entire system has stoppeddecreasing or until the error rate has reached a target level. Afterlearning, the DCN may be presented with new images (e.g., the speedlimit sign of the image 226) and a forward pass through the network mayyield an output 222 that may be considered an inference or a predictionof the DCN.

Deep belief networks (DBNs) are probabilistic models comprising multiplelayers of hidden nodes. DBNs may be used to extract a hierarchicalrepresentation of training data sets. A DBN may be obtained by stackingup layers of Restricted Boltzmann Machines (RBMs). An RBM is a type ofartificial neural network that can learn a probability distribution overa set of inputs. Because RBMs can learn a probability distribution inthe absence of information about the class to which each input should becategorized, RBMs are often used in unsupervised learning. Using ahybrid unsupervised and supervised paradigm, the bottom RBMs of a DBNmay be trained in an unsupervised manner and may serve as featureextractors, and the top RBM may be trained in a supervised manner (on ajoint distribution of inputs from the previous layer and target classes)and may serve as a classifier.

Deep convolutional networks (DCNs) are networks of convolutionalnetworks, configured with additional pooling and normalization layers.DCNs have achieved state-of-the-art performance on many tasks. DCNs canbe trained using supervised learning in which both the input and outputtargets are known for many exemplars and are used to modify the weightsof the network by use of gradient descent methods.

DCNs may be feed-forward networks. In addition, as described above, theconnections from a neuron in a first layer of a DCN to a group ofneurons in the next higher layer are shared across the neurons in thefirst layer. The feed-forward and shared connections of DCNs may beexploited for fast processing. The computational burden of a DCN may bemuch less, for example, than that of a similarly sized neural networkthat comprises recurrent or feedback connections.

The processing of each layer of a convolutional network may beconsidered a spatially invariant template or basis projection. If theinput is first decomposed into multiple channels, such as the red,green, and blue channels of a color image, then the convolutionalnetwork trained on that input may be considered three-dimensional, withtwo spatial dimensions along the axes of the image and a third dimensioncapturing color information. The outputs of the convolutionalconnections may be considered to form a feature map in the subsequentlayer, with each element of the feature map (e.g., 220) receiving inputfrom a range of neurons in the previous layer (e.g., feature maps 218)and from each of the multiple channels. The values in the feature mapmay be further processed with a non-linearity, such as a rectification,max(0,x). Values from adjacent neurons may be further pooled, whichcorresponds to down sampling, and may provide additional localinvariance and dimensionality reduction. Normalization, whichcorresponds to whitening, may also be applied through lateral inhibitionbetween neurons in the feature map.

The performance of deep learning architectures may increase as morelabeled data points become available or as computational powerincreases. Modern deep neural networks are routinely trained withcomputing resources that are thousands of times greater than what wasavailable to a typical researcher just fifteen years ago. Newarchitectures and training paradigms may further boost the performanceof deep learning. Rectified linear units may reduce a training issueknown as vanishing gradients. New training techniques may reduceover-fitting and thus enable larger models to achieve bettergeneralization. Encapsulation techniques may abstract data in a givenreceptive field and further boost overall performance.

FIG. 3 is a block diagram illustrating a deep convolutional network 350.The deep convolutional network 350 may include multiple different typesof layers based on connectivity and weight sharing. As shown in FIG. 3E,the deep convolutional network 350 includes the convolution blocks 354A,354B. Each of the convolution blocks 354A, 354B may be configured with aconvolution layer (CONV) 356, a normalization layer (LNorm) 358, and amax pooling layer (MAX POOL) 360.

The convolution layers 356 may include one or more convolutionalfilters, which may be applied to the input data to generate a featuremap. Although only two of the convolution blocks 354A, 354B are shown,the present disclosure is not so limiting, and instead, any number ofthe convolution blocks 354A, 354B may be included in the deepconvolutional network 350 according to design preference. Thenormalization layer 358 may normalize the output of the convolutionfilters. For example, the normalization layer 358 may provide whiteningor lateral inhibition. The max pooling layer 360 may provide downsampling aggregation over space for local invariance and dimensionalityreduction.

The parallel filter banks, for example, of a deep convolutional networkmay be loaded on a CPU 102 or GPU 104 of an SOC 100 to achieve highperformance and low power consumption. In alternative aspects, theparallel filter banks may be loaded on the DSP 106 or an ISP 116 of anSOC 100. In addition, the deep convolutional network 350 may accessother processing blocks that may be present on the SOC 100, such assensor processor 114 and navigation module 120, dedicated, respectively,to sensors and navigation.

The deep convolutional network 350 may also include one or more fullyconnected layers 362 (FC1 and FC2). The deep convolutional network 350may further include a logistic regression (LR) layer 364. Between eachlayer 356, 358, 360, 362, 364 of the deep convolutional network 350 areweights (not shown) that are to be updated. The output of each of thelayers (e.g., 356, 358, 360, 362, 364) may serve as an input of asucceeding one of the layers (e.g., 356, 358, 360, 362, 364) in the deepconvolutional network 350 to learn hierarchical feature representationsfrom input data 352 (e.g., images, audio, video, sensor data and/orother input data) supplied at the first of the convolution blocks 354A.The output of the deep convolutional network 350 is a classificationscore 366 for the input data 352. The classification score 366 may be aset of probabilities, where each probability is the probability of theinput data including a feature from a set of features.

Example Probabilistic Generative Model for Forecasting Subject Body Poseand Motion Intent

As used herein, a “subject” generally refers to a human, another type ofanimal, a machine implemented with joints for motion (e.g., a cyborg orother robots), or a representation thereof (e.g., an image of a human).Predicting subject motion may be used in a variety of environments. Forexample, in autonomous driving applications, predictions of subjectmotion may be used to anticipate pedestrian movement intent (e.g.,whether a pedestrian in the field of vision of one or more cameras on anautonomous vehicle is going to move and cause a collision with theautonomous vehicle). In augmented reality applications, predictions ofsubject motion may be used to display, to a user of an augmented realityapplication, the predicted location and movement of another subject overtime. In still and/or video capture scenarios, predicted subject motionmay be used to adjust a focus point such that a subject remains in focuswhile still or video footage is captured. In still other examples,predicted human motion may be used in human-robot interaction to causeactuators or other movement mechanisms on a robot to prepare for motionin a particular direction.

Conventionally, subject motion may be predicted using discriminativemappings over time. Regressive models may be used to predict subjectmotion, and these regressive models may predict an absolute coordinatein an image frame at which a joint may be located at a future point intime. However, regressive models may not account for the uncertainty offuture movements, various plausible future poses that may result from anobserved pose, the complexity of subject body motion, occlusion ofjoints in captured images, false detections of joints, and the like.Further, recurrent models may accumulate an amount of error over time.Because discriminative models can use predicted joint locations at onepoint in time to predict joint locations at a future point in time,noisy and potentially inaccurate predictions may be used to predictfuture joint locations. The accumulation of noise and inaccuratepredictions over the long term may result in poor predictions of futuresubject motion and joint distribution.

To improve the accuracy of predicted subject body poses and motionintent, aspects of the present disclosure provide for the generation ofsubject pose trees and training of a convolutional neural network (e.g.,an autoregressive deep neural network) using subject pose trees togenerate a probabilistic model. The probabilistic model generates aprobability distribution identifying a likelihood that a joint islocated at a particular location on an axis in space at a given time,and the probability distributions may be used to generate heatmaps andcolorized images representing joint motion. These colorized images maybe used to predict a subject pose (e.g., based on the relative positionsof each joint of the subject in an image) and a movement intent from thepredicted pose, and a variety of applications can take one or moreactions based on the predicted movement intent. By generating andapplying probabilistic models for predicting subject motion usingsubject pose trees, aspects of the present disclosure may account forthe uncertainty of plausible future poses in predicting subject motionand may infer such motion in real-time.

FIG. 4 illustrates an example subject pose, a subject pose tree, andtwo-dimensional tensors generated to represent the subject pose,according to aspects described herein. As illustrated, a subject pose410 may be represented as a series of joints connected to each other.Subject pose 410 may have a root joint that the other joints in thesubject pose are directly or indirectly connected to. For example, JointA may be the root joint for the subject and may represent the neck.Joints B, C, D, and E are connected directly to Joint A. Joints B and Emay represent the right and left shoulders, for example, whereas JointsC and D may represent the right and left hips, respectively. Joints F,G, H, and I are connected with Joint A through Joints B, C, D, and E,respectively. Joints F and I may represent the right and left elbows,for example, whereas Joints G and H may represent the right and leftknees, respectively. Finally, each of Joints J, K, L, and M in subjectpose 410 is connected with Joint A through two other joints, as shown.Joints J and M may represent the right and left wrists, for example,whereas Joints K and L may represent the right and left ankles,respectively. Because of the structure of the joint relationships insubject pose 410, it may be determined a priori that the movement ofJoints B, C, D, and E may depend on the movement of Joint A; themovement of Joints F, G, H, and I may depend on the movement of JointsB, C, D, and E, respectively; and the movement of Joints J, K, L, and Mmay depend on the movement of Joints F, G, H, and I, respectively.

Based on these determinations, a subject pose tree 420 may be generatedto represent the dependencies of the joints in subject pose 410. Thesubject pose tree 420 may be structured such that the level of thesubject pose tree 420 at which a joint is located may indicate thatjoint's immediate parent joint. For example, as illustrated, Joint Arepresents the root node in subject pose tree 420, as Joint A is notconnected to any parent joint and serves as the ultimate parent joint tothe other joints in subject pose 410. Joints B, C, D, and E areconnected directly to Joint A in subject pose tree 420, representingjoints that are directly connected to Joint A in subject pose 410. Thenext level of subject pose tree 420 represents joints that are connectedwith Joint A (the root node in subject pose tree 420) through anintermediary joint (e.g., Joints F, G, H, and I). Finally, the bottomlevel of subject pose tree 420 represents joints that are connected withJoint A (the root node in subject pose tree 420) through twointermediary joints.

While subject pose tree 420 may be useful in representing thedependencies of joints captured in subject pose 410, the structure ofsubject pose tree 420 may not be conducive for use in trainingprobabilistic models for predicting subject motion. Thus, subject posetree 420 may be transformed into a two-dimensional tensor 430representing the data and dependencies illustrated in subject pose tree420. The two-dimensional tensor 430 may also be referred to as atwo-dimensional matrix. As illustrated, two-dimensional tensor 430includes a plurality of rows and a plurality of columns. Each row mayrepresent a different level in subject pose tree 420. For example, row 1in two-dimensional tensor 430 may represent the root node (e.g., JointA) in subject pose tree 420, row 2 in two-dimensional tensor 430 mayrepresent the nodes at the second level of subject pose tree 420 (e.g.,Joints B, C, D, and E), row 3 in two-dimensional tensor 430 mayrepresent the nodes at the third level of subject pose tree 420 (e.g.,Joints F, G, H, and I), and so on. More generally, the n^(th) row intwo-dimensional tensor 430 may represent the nodes in level ii ofsubject pose tree 420.

Each column in two-dimensional tensor 430 generally identifies asequence of joint dependencies from a first joint to an N^(th) joint.Because each row represents nodes at an n^(th) level of subject posetree 420, each column may identify a series of joints in order from aroot node to the joint furthest away from the root node. This series ofjoints may preserve joint dependencies identified in the subject posetree. To generate a set of data for use in training a probabilisticmodel for predicting subject motion, the locations (e.g., in terms of animage pixel coordinate along an axis of the image) of each joint may beinserted at the appropriate location in the two-dimensional tensor 430,one tensor per axis of the image space. For example, in a scenario wheresubject pose 410 represents a human pose, each entry in the first row oftwo-dimensional tensor 430 may represent a location of the subject'sneck. Assuming the subject is posed facing away from the viewpoint(e.g., the camera), the remaining entries in a first column oftwo-dimensional tensor 430 may represent locations of the subject's leftshoulder, left elbow, and left wrist; the entries in a second column oftwo-dimensional tensor 430 may represent locations of the subject's lefthip, left knee, and left ankle; the entries in a third column oftwo-dimensional tensor 430 may represent locations of the subject'sright hip, right knee, and right ankle; and the entries in a fourthcolumn of two-dimensional tensor 430 may represent locations of thesubject's right shoulder, right elbow, and right wrist.

FIG. 5 illustrates an example joint generative model architecture 500used in generating a probabilistic model for predicting subject motionbased on the structure of subject pose tree 420, represented bytwo-dimensional tensor 430. Joint generative model 500 may be based onauto-regressive models and may be configured as a generative model thattakes the uncertainty of plausible future poses into account ingenerating probability distributions estimating future subject motionand joint location.

As illustrated, joint generative model 500 may be based on a stack ofthree-dimensional (3D) convolutional layers. A rectified output of afirst masked 3D convolutional layer 502 processed through a firstrectified linear unit (ReLU) 503, may be input into a summation function507 and may additionally be input into a second masked 3D convolutionallayer 504. The output of the second masked 3D convolutional layer 504may be processed through a second ReLU 505, and the output of the secondReLU 505 may be processed through a third masked 3D convolutional layer506. The output of the third masked 3D convolutional layer 506 may beprovided to summation function 507, and the summation of the rectifiedoutput of the first 3D convolutional layer 502 and the output of thethird masked 3D convolutional layer 506 may be provided as input to afourth masked 3D convolutional layer 508. The output of the fourthmasked 3D convolutional layer 508 may be processed through a softmaxfunction 509, discussed above, to result in a trained probabilisticmodel that generates probability distributions for the position of ajoint along an axis in space. As discussed, the inputs into the firstmasked 3D convolutional layer 502 may include a two-dimensional tensor430 for each axis along which a prediction of joint position and motionmay be requested.

The convolutional layers 502, 504, 506, and 508 may use a kernel size of5×3×3, for example, such that the convolutional layers examine a depthof five frames over a 3×3 space. More or less than five frames may beused. The 3×3 space may be configured to represent directional movementof a joint over a two-dimensional plane (e.g., the joint can move ineight different directions: up, down, left, right, and diagonals betweenthese four different directions). If a joint location remains the same(e.g., in the center of the 3×3 space) across different frames, aconvolutional layer 502 can infer that the joint has not moved.Otherwise, if a joint location changes across different frames, the newlocation of the joint in the 3×3 space may indicate a direction ofmovement.

As discussed, some convolution layers may be followed by rectifiedlinear unit (ReLU) non-linearity. In some aspects, the lastconvolutional layer of each residual block may not be followed by ReLUnon-linearity. The joint generative model 500 may generate 24 featuremaps for each convolutional layer other than the last convolutionallayer, and the last layer of the joint generative model 500 may producea number N of feature maps corresponding to the height and width of theframe.

In some aspects, the feature maps may be partially masked-out withthree-dimensional masks 600, illustrated in FIG. 6. The masks 600 arereferred to as three-dimensional, since the masks are two-dimensional inspace (e.g., 3×3), but cover a sequence of frames in time (e.g., 5frames), where time is the third dimension here. The first convolutionallayer (e.g., convolutional layer 502) may be masked with a first mask,designated Mask F for “first,” and the other convolutional layers (e.g.,layers 504, 506, and 508) may be masked with a second mask, designatedMask 0 for “other.” By masking the convolutional layers, jointgenerative model 500 may learn the dependencies between joints insubject pose tree 420 over time. Further, masking the convolutionallayers using three-dimensional masks 600 may restrict connections in thejoint generative model 500 to specific dependencies between joints insubject pose tree 420 (e.g., so that the joint generative model 500 doesnot infer dependencies between unrelated joints). The masks, asillustrated, may be applied spatially and temporally (e.g., acrossdifferent frames).

As illustrated, Mask F in the set of three-dimensional masks 600 may bemasked such that the first convolutional layer in joint generative model500 is unable to examine input data points at the current time t. Theother convolutional layers in joint generative model 500 may examine afeature space and thus may be allowed to look at input data points andfeature maps. In some aspects, while training joint generative model500, the convolutional layers in joint generative model 500 may beconfigured to look at the joint masks at time points (t−2), (t−1), and tto learn how a joint moves over time. Further, at time points (t−2) and(t−1), joint generative model 500 may examine the location of a joint,and to learn spatial and temporal dependencies between related joints(e.g., the joint and a parent joint), the joint generative model 500 mayexamine the location of the joint and the parent joint at time r. Whiletraining joint generative model 500, the convolutional layers of jointgenerative model 500 need not examine masks associated with time points(t+1) and (t+2) (e.g., infer positions of joints in the future);however, at inference time, joint generative model 500 may be configuredto examine the masks from time point (t−2) to time point (t+2) topredict joint movement and location one-by-one from a parent joint toits child joints.

During inference processes to predict the joint location and motion,partially available subject pose trees may be provided to jointgenerative model 500 as input. Joint generative model 500 may beconfigured to probabilistically generate future subject pose trees basedon the partially available subject pose trees. Subject pose trees may begenerated for a specific time point sequentially, row-by-row (e.g.,generating pose trees by predicting probable locations of the root jointin the subject pose tree 420, then immediate child joints of the rootjoint, then successively lower levels of joints until the probablelocations of each joint in subject pose tree 420 are determined).

FIG. 7 illustrates example operations for generating a probabilisticmodel for predicting subject motion, according to aspects describedherein. As illustrated, operations 700 begin at block 702, where asystem receives training data comprising a set of subject pose trees.The set of subject pose trees may comprise a plurality of subsets ofsubject pose trees. Each subset of subject pose trees may be associatedwith an image in a sequence of images depicting the subject. Eachsubject pose tree in the subset may be associated with an axis of theimage and may indicate a location along the axis of the image at whicheach of a plurality of joints of the subject is located.

At block 704, the system processes the received training data in aconvolutional neural network to generate a trained probabilistic modelfor predicting joint distribution and subject motion based on densityestimation. Density estimation in probability and statistics is thegeneration of an estimate, based on observed data, of an unobservableunderlying probability density function. Here, density estimationtechniques may allow for the prediction of joint distribution andsubject motion by generating probability distributions representing alikelihood of a joint being located at each position along an axis of animage at a given point in time. As discussed in further detail below,the trained probabilistic model may generate a probability distributionfor the position of a joint from an input of previously captured motionactivity. The probability distribution may be generated as an estimateof a percentage of projections including the joint at a particularlocation on an axis in space.

At block 706, the system deploys the trained probabilistic model to acomputer vision system. The trained probabilistic model may beconfigured to generate a probability distribution for each joint. Theprobability distribution generated by the trained probabilistic modelmay indicate a likelihood that the joint will be located at eachlocation along the axis of the image.

In some aspects, the convolutional neural network may comprise anautoregressive deep neural network.

In some aspects, the system may process the received training data bygenerating, from each subject pose tree, a two-dimensional matrix havinga plurality of columns, wherein each column of the matrix represents asequence of joint dependencies from a first joint to an n^(th) joint andpreserves joint dependencies identified in the subject pose tree. Thetrained probabilistic model may be generated based on the generatedtwo-dimensional matrices.

In some aspects, each element in the two-dimensional matrix mayrepresent the location along an axis of a joint in the plurality ofjoints of the subject. Each element in the matrix may represent alocation along an axis of a joint in the plurality of joints of thesubject. In some aspects, a joint dependency in the sequence of jointdependencies may define a parent joint and an immediately adjacent jointdependent on the parent joint.

In some aspects, the convolutional neural network is configured toexamine a position of a joint at a plurality of time points prior to agiven point in time and examine the position of the joint and a positionof its parent joint at the given point in time to learn spatial andtemporal dependencies of the joint and the parent joint.

In some aspects, the convolutional neural network comprises a stack ofthree-dimensional convolutional layers. The stack of three-dimensionalconvolutional layers may comprise a first convolutional layer maskedagainst input data points and one or more other convolutional layersfollowing the first convolutional layer that are unmasked against theinput data points. In some aspects, the first convolutional layer andthe other convolutional layers are configured to use a kernelrepresenting possible directions in which a joint in the subject posetree can move.

The probabilistic model—trained using subject pose trees input into aconvolutional neural network as described herein—may provide improvedaccuracy relative to regressive models that predict joint location in arecurrent neural network. For example, the probabilistic modelsdescribed herein may predict joint positions with improved accuracyrelative to conventional models the further out predictions are made.The mean joint displacement of the predicted joint location versus theactual joint location, for example, after predicting joint locationabout one second into the future may be less than half the mean jointdisplacement of a prediction generated using a recurrent model. Further,the predictions generated by the probabilistic model described hereinmay be generated in near-real-time (e.g., for an input of frames at 30frames per second, within the duration of a frame), and the timeinvolved to predict subject motion and joint location may be independentof the size of the input frame.

The probabilistic models described herein may be used to forecast, orpredict, the intent of subject motion based on an observed set ofsubject motion. For example, for an image sequence of length T, it maybe desirable to determine the subject's motion intent in a time t thatis less than T, in some scenarios significantly less than T (t<<T). Suchpredictions may be made in autonomous vehicle applications, where adetermination of subject motion intent may need to be made in time totake action (e.g., applying the brakes of the autonomous vehicle, takingevasive action to drive around the subject, etc.) to avoid a collisionwith the subject. In another example, the predictions may be made inimage capture operations, where a determination of subject motion intentmay need to be made in an amount of time that minimizes an amount oftime in which the subject is out of focus.

Generally, the position of a subject's joints in three-dimensional spacemay be represented as a sequence of coordinates along the X, Y, and Zaxes (for use in a recurrent neural network for classification) or astrajectory images in which heatmaps are generated around a pair ofcoordinates and joint motion is colorized according to relative time(for use in a convolutional neural network for classification). Asdiscussed above, because regressive models may not be able to accuratelypredict joint location and future subject motion in the future due tocascading uncertainty, aspects of the present disclosure provide for thegeneration of heatmaps based on probability distributions of predictedjoint location along an axis in (image) space to predict subject motion.

FIG. 8 illustrates probability distributions for the predicted locationof a joint and a heatmap generated from the probability distributions,according to aspects of the present disclosure. To predict futuresubject motion and determine a motion intent associated with the futuresubject motion, probability distributions 810 may be generated for eachjoint using a probabilistic model (e.g., joint generative model 500described above). As illustrated, the probability distributions 810 mayinclude a first probability distribution illustrating a likelihood thata joint is located at a particular location along a first axis (e.g.,the X axis) and a second probability distribution illustrating alikelihood that a joint is located at a particular location along asecond axis (e.g., the Y axis). The first and second axes may beorthogonal. In some aspects, the probability distribution may representa relative location in an image frame at which a joint may be located(e.g., at 0-100 percent of the length of an axis) rather than anabsolute pixel location in the image frame to allow for any size ofimage (which may be downscaled by a computer vision system prior tobeing input into the probabilistic model) to be provided as input. Asillustrated, probability distributions 810 indicate that the joint forwhich probability distributions 810 were generated is likely to belocated at a position corresponding to between 60 and 80 of the lengthof the first axis and between 40 and 60 percent of the length of thesecond axis, with the highest probability location being at about 70percent of the length of the first axis and about 50 percent of thelength of the second axis. Based on probability distribution 810,heatmap 820 may be generated. Heatmap 820 generally illustrates alikelihood that a joint is located at a particular position in atwo-dimensional space (e.g., the X-Y plane) at a given time based on thecolor at any given location of the two-dimensional space. Darker colors(e.g., black or colors near RGB 0, 0, 0) may represent locations atwhich a joint is unlikely to be located, while brighter colors mayrepresent differing probabilities of the joint being located in aparticular location. In some aspects, the heatmap may be generated ingrayscale, with lighter shades of grey representing higher probabilitiesfor the location of a joint in a two-dimensional space. In some aspects,the heatmap may be generated in color, with brighter colors representinghigher probabilities for the location of a joint.

Based on the heatmaps generated by the probabilistic model describedherein, the joint may be colorized for a specific point in timeaccording to the equation:

${o(t)} = \left\lbrack {\frac{t}{T},1,\frac{t}{T}} \right\rbrack$

Given the colorized joint over time on different planes inthree-dimensional space (e.g., the X-Y plane 920, the Y-Z plane 930, andthe X-Z plane 940), a system can stack the colorized joints together toform a representation for the whole sequence of predicted jointpositions and subject motion over a period of time in the future, Eachdynamic image in the stack may represent motion of a particular joint ina particular plane, with different colors (illustrated in FIG. 9 asdifferent patterns in a dynamic image) in the dynamic image representingan order of joint motion over time. As illustrated, the stack ofcolorized joints 910 in FIG. 9 colorizes the joint with threetwo-dimensional tensors. Based on the colorized stack of dynamic images,projected on different planes in 3D space, a convolutional neuralnetwork can be used to determine and classify a predicted pose at afuture point in time and determine a motion intent based on theclassification of the predicted pose.

Classification of a predicted subject pose and determination of a motionintent from the classification of the predicted subject pose describedabove with respect to colorization of a joint over time may provide auseful visualization to a viewer or observer of a subject. However, itshould be recognized that techniques other than analyzing colorizedimages may be used to classify a predicted pose and determine a motionintent from the classification of the predicted pose. For example,numeric representations of probability may be used to predict a subjectpose, classify the predicted pose, and determine a motion intent fromthe classification.

FIG. 10 illustrates example operations for determining a motion intentusing a probabilistic model for predicting joint location and subjectmotion, according to aspects described herein. As illustrated,operations 1000 may begin at block 1002, where a system receives a setof images for use in predicting future subject motion. In some aspects,the system may downscale the received set of images to acceleratedeterminations of motion intent or to ensure that each image in thereceived set of images is the same size.

At block 1004, the system generates time-sequence data for the receivedset of images. The time-sequence data generally comprises an additionalset of subject pose trees for the received set of images. Each subjectpose tree in the time-sequence data represents positions of joints in aspecific image and comprises a two-dimensional tensor representingdependencies of joints in the subject pose tree, as discussed above.

At block 1006, the system predicts, for one or more future points intime, a position of each joint in the subject pose tree by applying atrained probabilistic model to the time-sequence data. The predictedposition of each joint may be based on a probability distributiongenerated by the trained probabilistic model from an analysis of thegenerated time-sequence data.

At block 1008, based on the predicted position of each joint in thesubject pose tree, the system generates a colorized stack of images. Asdiscussed, the colorized stack of images may be generated from heatmapsillustrating the predicted location of a joint in a two-dimensionalspace, and the colorized stack of images may include images representingjoint motion along an X-Y axis, joint motion along a Y-Z axis, and jointmotion along an X-Z axis.

At block 1010, the system classifies the predicted pose. At block 1012,the system determines a motion intent based on the classification of thepredicted pose.

In some aspects, the use of probability distributions generated by aprobabilistic model for predicting subject motion may result inincreased accuracy of predictions of subject motion. For example, theaccuracy of predicted subject motion and joint position may increasefrom under 20 percent accuracy for predictions generated by a regressivemodel to over 40 percent accuracy for predictions generated by theprobabilistic model described herein given observation of 20 percent ofa sequence of human motion. Because the accuracy of predicted subjectmotion may be higher for any given amount of observations, the predictedsubject motion generated by the probabilistic models described hereinmay improve forecasting of subject motion and subject intent and thusimprove the functioning of autonomous systems that use predictions ofsubject motion to take action (e.g., autonomous vehicles, roboticssystems, still and/or video capture systems, etc.). For example, basedon the determined motion intent, a system can control an autonomousvehicle (e.g., apply braking, acceleration, and/or steering inputs toavoid a collision with an observed subject). In another aspect, a systemcan adjust a focus location of a camera (e.g., adjust focus towards oraway from infinity focus or a closest focal distance of a lens coupledto the camera) based on the determined motion intent so that theobserved subject remains substantially in focus (e.g., within the circleof confusion) as the object subject moves within the field of view ofthe camera.

In some aspects, the system can downscale each image of the received setof images to a lower resolution. The additional set of subject posetrees may be generated from the downscaled images. The resolutionselected may be a resolution lower than that of the images received setof images that provides sufficient fidelity to allow for jointrecognition and generation of subject pose trees from the images.

In some aspects, positions of each joint in the subject pose tree may bepredicted on a per-joint basis. For each joint, a probabilitydistribution may be generated. The probability distribution generallyrepresents a likelihood of the joint moving to a position in an imagefield (e.g., an area captured by one or more cameras in an autonomoussystem). A system can generate a heatmap from the probabilitydistribution for each of a plurality of dimensions. Different colors inthe heatmap may represent different probability scores (or other valuesindicative of a likelihood that a joint is located at a particularlocation) for a particular position of the joint in each of theplurality of dimensions.

In some aspects, the colorized stack of images representing thepredicted pose at the future point in time may be generated on aper-joint basis. For each joint, the joint may be colorized based on thegenerated heatmaps. Colorization of the joint may be performed within aplurality of three-dimensional tensors. The colorized joints may bestacked to represent a sequence of probable joint motion. In someaspects, the plurality of three-dimensional tensors may include a firsttensor representing an x-y coordinate plane in three-dimensional space,a second tensor representing a y-z coordinate plane in three-dimensionalspace; and a third tensor representing an x-z coordinate plane inthree-dimensional space.

In some aspects, determining the motion intent based on a classificationof the predicted pose may include evaluating predicted poses for aplurality of future points in time.

FIG. 11 is a block diagram illustrating an exemplary softwarearchitecture 1100 that may modularize artificial intelligence (AI)functions. Using the architecture, applications may be designed that maycause various processing blocks of an SOC 1120 (for example a CPU 1122,a DSP 1124, a GPU 1126, and/or an NPU 1128) to support a parallel MCdropout function/procedure for run-time operation of an AI application1102, according to aspects of the present disclosure.

The AI application 1102 may be configured to call functions defined in auser space 1104 that may, for example, provide for the detection andrecognition of a scene indicative of the location in which the devicecurrently operates. The AI application 1102 may, for example, configurea microphone and a camera differently depending on whether therecognized scene is an office, a lecture hall, a restaurant, or anoutdoor setting such as a lake. The AI application 1102 may make arequest to compiled program code associated with a library defined in anAI function application programming interface (API) 1106. This requestmay ultimately rely on the output of a deep neural network configured toprovide an inference response based on video and positioning data, forexample.

A run-time engine 1108, which may be compiled code of a runtimeframework, may be further accessible to the AI application 1102. The AIapplication 1102 may cause the run-time engine, for example, to requestan inference at a particular time interval or triggered by an eventdetected by the user interface of the application. When caused toprovide an inference response, the run-time engine may in turn send asignal to an operating system in an operating system (OS) space 1110,such as a Linux Kernel 1112, running on the SOC 1120. The operatingsystem, in turn, may cause an MC dropout function to be performed on theCPU 1122, the DSP 1124, the GPU 1126, the NPU 1128, or some combinationthereof. The CPU 1122 may be accessed directly by the operating system,and other processing blocks may be accessed through a driver, such as adriver 1114, 1116, or 1118 for, respectively, the DSP 1124, the GPU1126, or the NPU 1128. In the exemplary example, the deep neural networkmay be configured to run on a combination of processing blocks, such asthe CPU 1122, the DSP 1124, and the GPU 1126, or may be run on the NPU1128.

The various illustrative circuits described in connection with aspectsdescribed herein may be implemented in or with an integrated circuit(IC), such as a processor, a digital signal processor (DSP), anapplication-specific integrated circuit (ASIC), a field-programmablegate array (FPGA), or other programmable logic device. A processor maybe a microprocessor, but in the alternative, the processor may be anyconventional processor, controller, microcontroller, or state machine. Aprocessor may also be implemented as a combination of computing devices,e.g., a combination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration.

It is also noted that the operational steps described in any of theexemplary aspects herein are described to provide examples. Theoperations described may be performed in numerous different sequencesother than the illustrated sequences. Furthermore, operations describedin a single operational step may actually be performed in a number ofdifferent steps. Additionally, one or more operational steps discussedin the exemplary aspects may be combined. It is to be understood thatthe operational steps illustrated in the flow diagrams may be subject tonumerous different modifications as will be readily apparent to one ofskill in the art. Those of skill in the art will also understand thatinformation and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

The present disclosure is provided to enable any person skilled in theart to make or use aspects of the disclosure. Various modifications tothe disclosure will be readily apparent to those skilled in the art, andthe generic principles defined herein may be applied to other variationswithout departing from the spirit or scope of the disclosure. Thus, thedisclosure is not intended to be limited to the examples and designsdescribed herein, but is to be accorded the widest scope consistent withthe principles and novel features disclosed herein.

1. A method for predicting subject motion, comprising: receivingtraining data comprising a set of subject pose trees, associated with asequence of images, wherein each subject pose tree indicates a locationalong an axis of an image in the sequence of images at which each of aplurality of joints of a subject is located; processing the receivedtraining data in a convolutional neural network to generate a trainedprobabilistic model for predicting joint distribution and subject motionbased on density estimation; and deploying the trained probabilisticmodel to a computer vision system, wherein the trained probabilisticmodel is configured to generate a probability distribution for eachjoint indicating a likelihood that the joint will be located at eachlocation along the axis.
 2. The method of claim 1, wherein theconvolutional neural network comprises an autoregressive deep neuralnetwork.
 3. The method of claim 1, wherein processing the receivedtraining data comprises: generating, from each subject pose tree, atwo-dimensional matrix having a plurality of columns, wherein eachcolumn of the two-dimensional matrix represents a sequence of jointdependencies from a first joint to an n^(th) joint and preserves jointdependencies identified in the subject pose tree; and generating thetrained probabilistic model based on the generated two-dimensionalmatrices.
 4. The method of claim 3, wherein each element in thetwo-dimensional matrix represents the location along the axis of a jointin the plurality of joints of the subject.
 5. The method of claim 3,wherein a joint dependency in the sequence of joint dependencies definesa parent joint and an immediately adjacent joint dependent on the parentjoint.
 6. The method of claim 1, wherein the convolutional neuralnetwork is configured to examine a position of a joint at a plurality oftime points prior to a given point in time and examine the position ofthe joint and a position of its parent joint at the given point in timeto learn spatial and temporal dependencies of the joint and the parentjoint.
 7. The method of claim 1, wherein the convolutional neuralnetwork comprises a stack of three-dimensional convolutional layersincluding a first convolutional layer masked against input data pointsand one or more other convolutional layers following the firstconvolutional layer that are unmasked against the input data points. 8.The method of claim 7, wherein the first convolutional layer and theother convolutional layers are configured to use a kernel representingpossible directions in which a joint in the subject pose tree can move.9. The method of claim 1, further comprising: receiving a set of imagesfor use in predicting future subject motion; generating time-sequencedata for the received set of images comprising two-dimensional tensorsgenerated from an additional set of subject pose trees for the receivedset of images representing positions of joints in an image of the set ofimages and preserving dependencies of joints in the subject pose tree;predicting, for one or more future points in time, a position of eachjoint in the subject pose tree by applying the trained probabilisticmodel to the time-sequence data, wherein the predicted position of eachjoint is based on a probability distribution generated by the trainedprobabilistic model; based on the predicted position of each joint inthe subject pose tree, generating a colorized stack of images;determining a predicted pose at a future point in time based on thecolorized stack of images; classifying the predicted pose; anddetermining a motion intent based on the classification of the predictedpose.
 10. The method of claim 9, further comprising: controlling anautonomous vehicle based on the determined motion intent.
 11. The methodof claim 9, further comprising: adjusting a focus location of a camerabased on the determined motion intent.
 12. The method of claim 9,further comprising: downscaling each image of the received set of imagesto a lower resolution, wherein the additional set of subject pose treesis generated from the downscaled images.
 13. The method of claim 9,wherein predicting the position of each joint in the subject pose treecomprises: for each joint: generating a probability distributionrepresenting a likelihood of the joint moving to a position in an imagefield; and generating a heatmap from the probability distribution foreach of a plurality of dimensions, wherein different colors in theheatmap represent different probability scores for a particular positionof the joint in each of the plurality of dimensions.
 14. The method ofclaim 13, wherein generating the colorized stack of images representingthe predicted pose at the future point in time comprises: for eachjoint: colorizing the joint based on the generated heatmaps within aplurality of three-dimensional tensors; and stacking the colorizedjoints to represent a sequence of probable joint motion.
 15. The methodof claim 14, wherein the plurality of three-dimensional tensorscomprises: a first tensor representing an x-y coordinate plane inthree-dimensional space; a second tensor representing a y-z coordinateplane in three-dimensional space; and a third tensor representing an x-zcoordinate plane in three-dimensional space.
 16. The method of claim 9,wherein determining the motion intent based on a classification of thepredicted pose comprises evaluating predicted poses for a plurality offuture points in time.
 17. An apparatus for predicting subject motion,comprising: at least one processor configured to: receive training datacomprising a set of subject pose trees associated with a sequence ofimages, wherein each subject pose tree indicates a location along anaxis of an image in the sequence of images at which each of a pluralityof joints of a subject is located, process the received training data ina convolutional neural network to generate a trained probabilistic modelfor predicting joint distribution and subject motion based on densityestimation, and deploy the trained probabilistic model to a computervision system, wherein the trained probabilistic model is configured togenerate a probability distribution for each joint indicating alikelihood that the joint will be located at each location along theaxis; and a memory coupled to the processor.
 18. The apparatus of claim17, wherein the convolutional neural network comprises an autoregressivedeep neural network.
 19. The apparatus of claim 17, wherein the at leastone processor is configured to process the received training data by:generating, from each subject pose tree, a two-dimensional matrix havinga plurality of columns, wherein each column of the two-dimensionalmatrix represents a sequence of joint dependencies from a first joint toan n^(th) joint and preserves joint dependencies identified in thesubject pose tree; and generating the trained probabilistic model basedon the generated two-dimensional matrices.
 20. The apparatus of claim17, wherein the convolutional neural network is configured to examine aposition of a joint at a plurality of time points prior to a given pointin time and examine the position of the joint and a position of itsparent joint at the given point in time to learn spatial and temporaldependencies of the joint and the parent joint.
 21. The apparatus ofclaim 17, wherein the convolutional neural network comprises a stack ofthree-dimensional convolutional layers including a first convolutionallayer masked against input data points and one or more otherconvolutional layers following the first convolutional layer that areunmasked against the input data points.
 22. The apparatus of claim 17,wherein the at least one processor is further configured to: receive aset of images for use in predicting future subject motion; generatetime-sequence data for the received set of images comprisingtwo-dimensional tensors generated from an additional set of subject posetrees for the received set of images representing positions of joints inan image of the set of images and preserving dependencies of joints inthe subject pose tree; predict, for one or more future points in time, aposition of each joint in the subject pose tree by applying the trainedprobabilistic model to the time-sequence data, wherein the predictedposition of each joint is based on a probability distribution generatedby the trained probabilistic model; based on the predicted position ofeach joint in the subject pose tree, generate a colorized stack ofimages; determine a predicted pose at a future point in time based onthe colorized stack of images; classify the predicted pose; anddetermine a motion intent based on the classification of the predictedpose.
 23. The apparatus of claim 22, wherein the at least one processoris configured to predict the position of each joint in the subject posetree by: for each joint: generating a probability distributionrepresenting a likelihood of the joint moving to a position in an imagefield; and generating a heatmap from the probability distribution foreach of a plurality of dimensions, wherein different colors in theheatmap represent different probability scores for a particular positionof the joint in each of the plurality of dimensions.
 24. The apparatusof claim 23, wherein the at least one processor is configured togenerate the colorized stack of images representing the predicted poseat the future point in time by: for each joint: colorizing the jointbased on the generated heatmaps within a plurality of three-dimensionaltensors; and stacking the colorized joints to represent a sequence ofprobable joint motion.
 25. The apparatus of claim 24, wherein theplurality of three-dimensional tensors comprises: a first tensorrepresenting an x-y coordinate plane in three-dimensional space; asecond tensor representing a y-z coordinate plane in three-dimensionalspace; and a third tensor representing an x-z coordinate plane inthree-dimensional space.
 26. The apparatus of claim 22, wherein the atleast one processor is configured to determine the motion intent basedon the classification of the predicted pose by evaluating predictedposes for a plurality of future points in time.
 27. An apparatus forpredicting subject motion, comprising: means for receiving training datacomprising a set of subject pose trees is associated with a sequence ofimages, wherein each subject pose tree indicates a location along anaxis of an image in the sequence of images at which each of a pluralityof joints of a subject is located; means for processing the receivedtraining data in a convolutional neural network to generate a trainedprobabilistic model for predicting joint distribution and subject motionbased on density estimation; and means for deploying the trainedprobabilistic model to a computer vision system, wherein the trainedprobabilistic model is configured to generate a probability distributionfor each joint indicating a likelihood that the joint will be located ateach location along the axis.
 28. The apparatus of claim 27, wherein themeans for processing the received training data comprises: means forgenerating, from each subject pose tree, a two-dimensional matrix havinga plurality of columns, wherein each column of the two-dimensionalmatrix represents a sequence of joint dependencies from a first joint toan n^(th) joint and preserves joint dependencies identified in thesubject pose tree; and means for generating the trained probabilisticmodel based on the generated two-dimensional matrices.
 29. The apparatusof claim 27, further comprising: means for receiving a set of images foruse in predicting future subject motion; means for generatingtime-sequence data for the received set of images comprisingtwo-dimensional tensors generated from an additional set of subject posetrees for the received set of images representing positions of joints inan image of the set of images and preserving dependencies of joints inthe subject pose tree; means for predicting, for one or more futurepoints in time, a position of each joint in the subject pose tree byapplying the trained probabilistic model to the time-sequence data,wherein the predicted position of each joint is based on a probabilitydistribution generated by the trained probabilistic model; means forgenerating a colorized stack of images based on the predicted positionof each joint in the subject pose tree; means for determining apredicted pose at a future point in time based on the colorized stack ofimages; means for classifying the predicted pose; and means fordetermining a motion intent based on the classification of the predictedpose.
 30. A non-transitory computer-readable medium having instructionsstored thereon which, when executed by at least one processor, performan operation for predicting subject motion, the operation comprising:receiving training data comprising a set of subject pose treesassociated with a sequence of images, wherein each subject pose tree inthe subset is associated with an axis of the image and indicates alocation along an axis of an image in the sequence of images at whicheach of a plurality of joints of a subject is located; processing thereceived training data in a convolutional neural network to generate atrained probabilistic model for predicting joint distribution andsubject motion based on density estimation; and deploying the trainedprobabilistic model to a computer vision system, wherein the trainedprobabilistic model is configured to generate a probability distributionfor each joint indicating a likelihood that the joint will be located ateach location along the axis.